Abhigyan Dasgupta

Polar crystals composed of charged ionic planes cannot exist in nature without acquiring surface changes to balance an ever-growing dipole. The necessary changes can manifest structurally or electronically. An electronic asymetry has long been observed in the LaAlO3/SrTiO3 system. Electron accumulation is observed near the LaAlO3/TiO2-SrTiO3 interface, while the LaAlO3/SrO-SrTiO3 stack is insulating. Here, we observe evidence for an asymmetry in the surface chemical termination for nominally stoichiometric LaAlO3 films in contact with the two different surface layers of SrTiO3 crystals, TiO2 and SrO. Using several element specific probes, we find that the surface termination of LaAlO3 remains AlO2 irrespective of the starting termination of SrTiO3 substrate surface. We use a combination of cross-plane tunneling measurements and first principles calcula- tions to understand the effects of this unexpected termination on band alignments and polarity compensation of LaAlO3/SrTiO3 heterostructures. An asymmetry in LaAlO3 polarity compensation and resulting electronic properties will fundamentally limit atomic level control of oxide heterostructures.

ChatGPT is a cutting-edge artificial intelligence technology that was released for public use in November 2022. Its rapid adoption has raised questions about capabilities, limitations, and risks. This article presents an overview of ChatGPT, and it highlights the current state of this technology for the medical field. The article seeks to provide a balanced perspective on what the model can and cannot do in three specific domains: clinical practice, research, and medical education. It also provides suggestions on how to optimize the use of this tool.

Among the many challenges arising from the high luminosities of the HL-LHC is the impact of increased hit rates in the cathode strip chambers of the CMS endcap muon system.These chambers detect muons as part of the CMS muon trigger, and their data is used offline for muon track reconstruction.Neutrons (both fast and thermal) induce background hits via nuclear interactions and capture, followed by gamma emission and (mainly) Compton scatter off electrons that subsequently ionize the chamber gas.This note presents recent efforts to improve the understanding of such neutron-induced background through detailed comparison of CMS pp collision data and GEANT4 simulation.

The U.S. Securities and Exchange Commission (SEC) mandates all public companies to file periodic financial statements that should contain numerals annotated with a particular label from a taxonomy. In this paper, we formulate the task of automating the assignment of a label to a particular numeral span in a sentence from an extremely large label set. Towards this task, we release a dataset, Financial Numeric Extreme Labelling (FNXL), annotated with 2,794 labels. We benchmark the performance of the FNXL dataset by formulating the task as (a) a sequence labelling problem and (b) a pipeline with span extraction followed by Extreme Classification. Although the two approaches perform comparably, the pipeline solution provides a slight edge for the least frequent labels.

A fast-emerging topic, Sign Language Recognition(SLR) focuses on creating technologies that allow computers to interpret sign language. In order to bridge gaps in communication between the hearing and deaf populations and to improve accessibility for those who are deaf, sign language should be acknowledged. These systems can precisely recognise sign language by detecting and tracking hand gestures, face expressions, and body language. The goal of this paper is to provide researchers with a thorough understanding of current SLR technology. To ensure a thorough and accurate analysis, the evaluation includes a number of literature sources, which are academic journals, conferences, and proceedings. The analysis underlines the need for consistent evaluation methodologies and standards and also discusses the datasets and evaluation metrics that are currently available for sign language recognition. Lastly, the report concludes the existing limitations of SLR and offers a roadmap for future possibilities in SLR.

Many physical effects can produce unstable plasma behavior that affect K‐shell emission from arrays. Such effects include: asymmetry in the initial density profile, asymmetry in power flow, thermal conduction at the boundaries, and non‐uniform wire ablation. Here we consider how asymmetry in the radiation field also contributes to the generation of multidimensional plasma behavior that affects K‐shell power and yield. To model this radiation asymmetry, we have incorporated into the MACH2 r‐z MHD code a self‐consistent calculation of the non‐LTE population kinetics based on radiation transport using multi‐dimensional ray tracing. Such methodology is necessary for modeling the enhanced radiative cooling that occurs at the anode and cathode ends of the pinch during the run‐in phase of the implosion. This enhanced radiative cooling is due to reduced optical depth at these locations producing an asymmetric flow of radiative energy that leads to substantial disruption of large initial diameter (>5 cm) pinches and drives 1D into 2D fluid (i.e., Rayleigh‐Taylor like) flows. The impact of this 2D behavior on K‐shell power and yield is investigated by comparing 1D and 2D model results with data obtained from a series of single wire array stainless steel experiments performed on the Z generator.

A 1D Lagrangian magnetohydrodynamic z‐pinch simulation code is extended to include wire ablation. The plasma transport coefficients are calibrated to reproduce the K‐shell yields measured on the Z generator for three stainless steel arrays of diameter 55 mm and masses ranging from 1.8 to 2.7 mg. The resulting 1D scaling model is applied to a larger SS array (65 mm and 2.5 mg) on the refurbished Z machine. Simulation results predict a maximum K‐shell yield of 77 kJ for an 82 kV charging voltage. This maximum drops to 42 kJ at 75 kV charging. Neglecting the ablation precursor leads to a ∼10% change in the calculated yield.

AASC is designing multiple-shell gas puff loads for Z. Here we assess the influence of the loads initial gas distribution on its K-shell yield performance. Emphasis is placed on designing an optimal central jet initial gas distribution, since it is believed to have a controlling effect on pinch stability, pinch conditions, and radiation physics. We are looking at distributions that optimize total Ar K-shell emission and high energy (>10 KeV) continuum radiation. This investigation is performed with the Mach2 MHD code with non-LTE kinetics and ray trace based radiation transport.

A series of Al/Mg nested wire array Z-pinch load experiments has been recently performed on the refurbished Z accelerator. The earlier comparison study of the results from ID and 2D radiation MHD simulations of the Sandia Z1907/1908 experiments [Y. K. Chong, et. al, APS09] has shown that, in addition to the substantial difference in the prediction capability of the ID and 2D models, the radiation physics and implosion dynamics of the plasmas are significantly affected by the nonuniform structures and inhomogenities. In this study, we extend the mass scaling analysis of the radiation for 50mm diameter arrays through a detailed investigation of the complex nonlinear interaction dynamics between the multidimensional structures and the ambient radiation, and the resulting effects on the radiation plasma ensemble. In particular, we focus on the temporal and spatial evolution of the mass, momentum and energy flow distribution under the driving force field, and of the radiation emission and nonlocal transport processes. The study will employ the mach MHD codes with an improved dynamical domain TCRE (DDTCRE) transport [Y. K. Chong, et. al, ICOPS 2005] which affords a much greater flexibility and capacity in the grid resolution and the physics detail. The investigation is further aided through the detailed postprocess analysis of the K- and L-shell radiation yield and power signatures, as well as the spectral and spatial characteristics of the radiation during the various stages of the Z-pinch implosion process using the AXSTRAN, a 2D self-consistent non-LTE radiation ionization dynamics code with multifrequency integral transport and detailed configuration atomic model, in conjunction with the SPECAM 3D non-LTE spectra and image synthesizer code.

A 2D radiation MHD model has been developed to investigate stainless steel wire array implosion experiments on the Z and refurbished Z machines. This model incorporates within the Mach2 MHD code a self‐consistent calculation of the non‐LTE kinetics and ray trace based radiation transport. Such a method is necessary in order to account for opacity effects in conjunction with ionization kinetics of K‐shell emitting plasmas. Here the model is used to investigate multi‐dimensional effects of stainless steel wire implosions. In particular, we are developing techniques to produce non‐LTE, axially and/or radially resolved synthetic spectra based upon snapshots of our 2D simulations. Comparisons between experimental spectra and these synthetic spectra will allow us to better determine the state of the experimental pinches.

In recent years, there have been significant advances in instrumental capabilities for making X‐ray spectroscopic measurements of astrophysical plasmas. There have been corresponding improvements in X‐ray diagnostics for advanced multi‐mega‐ampere pulse power machines that produce increasingly large radiative yields from gas‐puff and wire array Z pinch plasmas. Analysis used for Z pinches can be used to study ICF and also astrophysical plasmas where laboratory measurements and simulations are the only means to interpret observed data. The astrophysical data for Fe, the most cosmically abundant high Z element, can provide a wealth of information about cosmic plasmas. Fe is also the key element in stainless steel (SS) wire arrays that are investigated as an intense X‐ray radiation source at the Z machine at Sandia National Laboratories. The implosion dynamics of an array of wires on the Z and/or refurbished Z accelerator produces an abundance of radiation from the K‐ and L‐shell ionization stages. These dynamic plasmas are inherently non‐LTE, with opacity and other factors influencing the X‐ray output. As the plasma assembles on axis, a number of time resolved snapshots provide temperature and density profiles and map the emitting region. We will analyze the ionization dynamics and generate K‐ and L‐shell spectra using the conditions generated in the Z and/or refurbished Z accelerator, described by a 1‐D non‐LTE radiation‐hydrodynamics model. Diagnostics based on spectral shape of L‐shell emissions are inherently more difficult than those based on K‐shell emissions because of more complex multiplet structures and line overlaps. The non‐LTE populations are obtained by using detailed atomic models that include all important excitation, ionization, and recombination processes. We will highlight the connection between laboratory Z‐pinch plasma simulations and astrophysical plasmas.

Experiments on the Z accelerator with nested stainless steel wire arrays produced K‐shell x‐ray yields exceeding 50 kJ in the energy range 5.5 to 8 keV. Stainless steel (Z = 24–28) can barely be ionized to the K‐shell on Z, and the spectra are therefore sensitive to the details of the implosion. We have simulated the implosion dynamics of stainless steel wire arrays with diameters ranging from 4.5 to 8.0 centimeters using a detailed configuration non‐LTE radiation hydrodynamics model. Reasonable agreement with total and K‐shell experimental yields was obtained for the various array configurations. A comparison is made between the 1‐D and 2‐D simulations for shot Z‐578.

Author(s): Dasgupta, Abhigyan | Advisor(s): Cousins, Robert D | Abstract: This thesis presents a search for new long-lived particles decaying to two muons in the CMS detector with pp collision data taken at sqrt(s) = 13 TeV corresponding to 36.3 fb-1 of integrated luminosity during Run 2 of the LHC. Such decays would appear as dimuon vertices displaced with respect to the pp interaction point. The search presented in this thesis uses only the muon system in order to probe the longest lifetimes to which the LHC experiments are sensitive. The results are interpreted in terms of a benchmark model consisting of exotic Higgs bosons decaying to long-lived scalar bosons, but are presented in an approximately model-independent way suitable for reinterpretation. No excess is observed. The appendix describes a study of neutron-induced background in CMS endcap muon chambers.